Underfeed control for percussion tool

ABSTRACT

A control valve for throttling the flow of motive air to a pneumatic percussion tool having a piston hammer reciprocably driven in a cylinder to strike a working implement. The control valve is responsive to a predetermined maximum pressure in an air cushion chamber formed between the piston hammer and the cylinder to throttle the flow of motive air to the tool when the working implement is not in proper blow-receiving position. Control air is communicated from the pneumatic cushion to operate the control valve; or, alternatively, a pilot valve may be used to sense a pressure signal from the cushion chamber to produce operation of the control valve.

United States Patent Hanson 1 1 Jan. 23, 1973 1 UNDERFEED CONTROL FOR 1,905,132 4/1933 Bishop etal ..91/445 PERCUSSIQN TOOL 3,376,791 4/1968 Ashfield et al. ...91 290 2,609,791 9/1952 Bohlman 91/284 [75] Inventor: Laurence B. Hanson, Pine, Colo. 1,057,701, 4/1913 Bayles "91/317 [73] Assigneez Gardnwnemer Company, Quincy, 1,494,030 5/1924 Slater ..91/317 L Primary ExaminerPaul E. Maslousky Filed: March 1971 Attorney-Michael E. Martin [2l] Appl. No.. 128,515 [57] ABSTRACT Related Application Data A control valve for throttling the flow of motive air to [63] Continuation of Ser. No. 833,431, June 16, 1969, a pneumatic percussion tool having a piston hammer abandfinedreciprocably driven in a cylinder to strike a working implement. The control valve is responsive to a [52] U.S.Cl. ..9l/220,91/290,9l/445 predetermined maximum pressure in an cushion 25/04, 25/04 chamber formed between the piston hammer and the Field of Search "91/445, cylinder to throttle the flow of motive air to the tool 91/335 446 when the working implement is not in proper blowreceiving position. Control air is communicated from [56] Reerences Cited the pneumatic cushion to operate the control valve; UNITED STATES PATENTS or, alternatively, a pilot valve may be used to sense a pressure signal from the cush1on chamber to produce 799,190 9/1905 Sage ..9l/220 operation of the control valve. 2,004,145 6/1935 Wineman ....9l/220 2,970,579 2/1961 Paris ..91/317 3 Claims, 2 Drawing Figures 76 74 32 72 70 I as V 7a- 9 25 25\ Z 5 as 34 e PATENTEUJAN 23 #915 antenna fi, Hamsnn again? 1 UNDERFEED CONTROL FOR PERCUSSION TOOL RELATED APPLICATION This application is a continuation of application Ser.

No. 833,431, filed June 16, I969, now abandoned.

BACKGROUND OF THE INVENTION .of motive air to opposed faces of the hammer. In such percussion tools an air cushion is normally formed by air trapped in the forward end of the cylinder by the hammer during the forward stroke thereof. If the working implement is not fed against the work, the blowreceiving end of the implement is usually driven out of blow-receiving contact with the hammer. Under such conditions, the blow-delivering stroke of the hammer is The present invention further provides, in an alternate embodiment, for control means including a pilot operated valve for supplying air from the motive air source to the control valve when the quantity of 5 compressed air available in the cushion chamber is inarrested by the aforementioned air cushion. The result- 3 ing compression of the cushion air is often great enough, with the tool operating at or near full throttle,

to cause temperatures which will result in the autogenous ignition of an air-oil mixture normally present in the cushion area. The presence of the air-oil mixture is due to the fact that in conventional pneumatic percussion tools the lubricating oil for the tool is introduced into thesupply of motive air to the percussion motor. 'The resultant heat and destructive forces. caused by the aforementioned ignition will quickly 1 damage the tool unless the motive air supply to the percussion motor is substantially throttled without delay. In many percussion tools the frequency of reciprocation of the hammer is so rapid that manual control of the tool to reduce the motive fluid supply cannot be achieved before damage from ignition in the cushion is encountered. Furthermore, in many applications a plurality of tools may be operating simultaneously and the operator is often unaware of the underfeed condition before a failure occurs due to overcompression in the cushion chamber.

Variousde'vices' are known in the art of percussion tools for throttling the flow of motive air to the tool in response to the'working implement being displaced out .ofj'blow-receiving position. U.S. PatrNo. 1,590,269 to CB. Wade and U.S Pat. application Ser No. 683,578

to A.W. Wallace respectively disclose mechanical and fluid operated means for sensing the displacement of the working implement to close a valve thereby throttling the supply of motive air to the tool.

SUMMARY OF THE INVENTION The present invention provides for control means operable in res'ponseto a predetermined pressure condition in the hammer-arresting cushion chamber of an air operated percussion tool to throttle the supply of motive air to the tool. A control valve, including a pressure fluid actuator," operates to reduce the supply of motive air to the tool percussion motor in response to a pressure signal from the hammer-arresting cushion of said motor. The control valve advantageously utilizes compressed air supplied directly from the cushion chamber through'a passage in the percussion motor housing.

. form of compressed air is admitted to the valve 24 from r sufficient to operate the control valve.

The present invention provides a mechanically uncomplicated and reliable means for preventing destructive force conditions and thermal degradation in fluid operated percussion tools thereby reducing the-hazards to persons operating such tools and preserving the structural integrity of tools so equipped.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a pressure fluid operated percussion tool, generally designated by the numeral 10, is illustrated in partial longitudinal section. The tool 10 is provided with a percussion motor comprising a housing 12 having a longitudinal cylindrical bore 14 in which a piston hammer 16 is reciprocably disposed. The cylinder 14 includes an exhaust port 15 for exhausting spent motive fluid from the "percussion motor. The piston hammer 16 includes opposed transverse faces 18 and 20, and a reduced diameter portion 22. The housing 12 also includes a fluid distributing valve 24 suitably retained therein by a backhead 26. The distributing valve 24 is of a well known type such as the general type of distributing valve disclosed in U.S. Pat. No. 2,100,541 to 13.6. Gartin and is operable to valve pressure fluid alternately to the opposed piston faces 18 and'20 to effect reciprocating motion of the piston hammer 16 within the bore 14. Pressure fluid in the a supply, not shown, by way of a supply line 28 threadedly connected to the backhead 26, and through passages 30, 32 and 34 into the space 36 adjacent the value.

The opposite end of the cylinder bore 14 is closed by an insert 37 having a transverse face 38 and a cylindri cal bore 40 which axially slidably journals the reduced diameter portion 22 of the piston hammer. The close fitting relationship between the bore 40 and the hammer portion 22 provides a substantial fluid seal. Thev insert 37 is retained in assembly with the housing 12 by a front head 42 which in turn is held secure in assembly with the housing 12 and backhead 26 by a pair of elongated bolts 44 in a manner well known. The

front head 42 includes a chuck member 46, and an end cap 48 threadedly engaged with the front head.

The chuck 46 includes a longitudinal bore 50 in which a working implement 52 is slidably disposed. The working implement includes an annular collar 54 engageable with the end cap 48 to limit the forward axial movement of the implement. The working implement 52 may be the shank portion of a rock drill rod or any suitable member adapted to transmit percussion blows to a work surface, not shown. When the tool 10 is being suitably forced or fed toward a work surface the implement 52 is axially shifted into blow-receiving relationship with the hammer 16 as shown in FIG. 1. However, in response to inadequate feed force being applied to the tool or breakage of a portion of the implement, the blow-receiving portion 53 is operable to move forward out of blow-receiving relationship with the hammer as shown by the dotted lines.

In communication with an air cushion chamber 56 formed by the cylinder bore 14 and the hammer 16 is a conduit 58 in the housing 12 which opens into a chamber 60 having a check valve 62 biasedto close the conduit 58 by a spring 64. A passage 66 extends from the chamber 60 to a passage 68 in a transversely fitted plug 70 in the backhead 26. The passage 68 is in fluid flow communication with a chamber 72 having means operable to reduce the flow of air to the percussion motor comprising a valve closure member 74 slidably housed in the chamber 72. The valve member 74 includes a pressure fluid actuator comprising a surface 76 responsive to pressure fluid admitted to the chamber 72 to move the member into a position to reduce or block the flow of pressure fluid from the passage 32 to the passage 34. A small orifice 78 in the plug 70 is operable to vent the chamber 72 to atmosphere.

As previously mentioned, the tool is operable to deliver percussive blows to the working implement 52 by valving compressed air alternately to opposite faces of the hammer 16. The hammer is driven forwardly on a blow-delivering stroke by valving air into the chamber 80. As the surface 18 of the hammer passes an opening 82 leading to a conduit 84 pressure air is supplied to a suitable mechanism in the valve 24 to interrupt the supply of air to chamber 80 and shift the valve tosupply air to chamber 56 by way of conduit 86. After the delivery of a blow to the implement 52 pressure air supplied to the chamber 56 operates to return the hammer toward the valve 24 whereby said valve again admits a quantity of motive air to chamber 80 to provide another blow-delivering stroke.

When an operating condition is encountered 'in which the tool and the implement are not being forced adequately toward the work surface, or if the implement should break, the blow-receiving portion 53 would be thrown forward out of contact with the hammer 16 to the position designated by the dotted lines. Under such a condition the kinetic energy imparted to the hammer by the motive air in chamber 80 would cause the hammer to travel past the conduit 86 toward the surface 38 trapping a quantity of air in the chamber 56 and compressing the trapped air until the forward motion of the hammer was arrested. In fact, under most operating conditions the blow-delivering "stroke is sufficient to cause substantial compression of the air trapped in the cushion chamber, should the implement 52 be displaced out of blow-receiving position. Accordingly, thermodynamic heating of the highly compressed air is often great enough to cause autogenous ignition of lubricating oil normally present on the hammer and cylinder surfaces and entrained with the trapped air. The resultant effect is not unlike the operation of a compression ignition type internal combustion engine. The hammer is reciprocated quite rapidly and with each stroke a fresh charge of oil laden air is introduced into the cushion chamber to be ignited unless the motive air supply to the tool is substantially reduced or shut off. Control means to prevent overcompression of the cushion air is provided by the check valve 62 and control valve 74. At a predetermined pressure in the cushion chamber 56 the valve 62 will open against the bias of spring 64 to provide flow of air from the cushion chamber to the chamber 72 through conduits 66 and 68 whereby pressure air acting on surface 76 will move the valve 74 to reduce the flow of supply air from passage 32 to the distributing valve 24.

When the proper rate of feed is restored to place the implement 52 back in blow-receiving position the hammer will strike the implement before the volume of chamber 56 is reduced sufficiently to compress the air trapped therein to a pressure greater than the supply pressure of air in conduit 86. Accordingly, the check valve will be moved to close by the spring 64 and' the chamber 72 will be vented through conduit 68 and orifice 78. Supply motive air acting on surface 88 of the control valve closure member 74 will then move the losure member to the position shown in FIG. 1 providing full flow of motive air to the tool percussion motor.

An alternate embodiment of the present invention is illustrated in FIG. 2. In the embodiment of FIG. 2 the pressure signal from the cushion chamber 56 is transmitted through a passage 90 having a spring biased check valve 92 in circuit therewith. The passage 90 is in communication with a pilot operator 94 of a two-posirtion valve 96 having an a and b position. The valve 96 is operable to be in communication with a modified control valve chamber 98 in the backhead 26 by way of a 'passage 100. Slidably disposed in the chamber 98 is a control valve closure member 102 having an actuator surface 104 responsive to pressure fluid admitted to the chamber 98-to cause the closure member to move to block the flow of motive air to passage 34. In the position a of the valve 96, the chamber 98 is vented and the lcontrol valve is in position to permit flow of air to the percussion motor through passages 32 and 34. However, in response to a predetermined pressure in the cushion chamber 56 the check valve 92 will open providing a pressure signal to shift the valve 96 to the position b whereby pressure air from the supply source will flow through conduit 106 and to the chamber 98 to move the value 102 to substantially throttle the flow of air to passage 34. When the pressure in the cushion chamber 56 is reduced to a value less than the check valve opening pressure, the conduit 90 is vented through the orifice 108 and the valve 96 shifts to position a venting the chamber 98 whereby supply air act- I ing on surface 110 of valve member 102 causes the same to open restoring flow to the percussion motor. Due to the use of air at supply pressure to close the valve 102, the actuator surface 104 must be greater in area than surface 110 and the chamber portion 112 must be vented through conduit 114. The source of pressure fluid to operate the valve member 102 may be other than the motive air supply in which case the relative sizes of areas 104 and 110 could be changed. The embodiment of FIG. 2 is particularly advantageously used in percussion tools of relatively small cylinder bore and hammer stroke dimensions wherein the volume of air trapped in the cushion chamber is not sufiicient to be used to operate the control valve actuator.

What is claimed is:

1. in a percussion tool: a pressure fluid operated percussion motor including a housing having a cylinder bore, a piston hammer having opposed piston faces disposed in said cylinder bore for reciprocating movement, fluid distributing means for alternately valving pressure fluid to said opposed piston faces, cushioning means including a cushion chamber formed by an end portion of said cylinder bore, said piston hammer and a transverse end face closing said cylinder bore;

pressure fluid supply means;

a pressure fluid actuated control valve interposed between said pressure fluid supply means and said percussion motor, said control valve including a chamber and a closure member having a pressure surface located in said chamber and responsive to the admission of pressure fluid to said chamber to actuate said closure member to reduce the flow of pressure fluid to said percussion motor;

passage means operable to be in communication with said cushion chamber for conducting pressure fluid from said cushion chamber to affect the admission of pressure fluid to said chamber; and,

'a check valve' interposed in said passage means and including biasing means operable to bias said check valve in a closed position, said check valve being responsive to a predetermined pressure in said cushion chamber to open to provide for conducting pressure fluid from said cushion chamber through said passage means to cause said control valve tooperate to, reduce the flow of pressure fluid to said percussion motor.

2. In a percussion tool:

a pneumatic percussion motor including a housing having a cylinder bore, a piston hammer having opposed piston faces disposed in said cylinder, bore for reciprocating movement, fluid distributing means for alternately valving pressure air to said opposed piston faces, cushioning means including a pneumatic cushion chamber formed by an end portion of said cylinder bore, said piston hammer and a transverse end face closing said cylinder bore;

a working member disposed to be in blow-receiving relationship with said piston hammer and axially shiftable to be out of blow-receiving relationship with said piston hammer;

pressure air supply means;

a fluid actuated control valve interposed between said pressure air supply means and said percussion motor, said control valve including a chamber and a closure member having a pressure surface located in said chamber and responsive to the admission-of pressure fluid to said chamber to actuate said closure member to reduce the flow of pressure air to said percussion motor;

i passage means operable to be in communication with l l l l l l l l said cushion chamber for conducting pressure air from said cushion chamber to affect the admission of pressure fluid to saidchamber; and, i

check valve interposed in said passage means responsive to a predetermined air pressurein said cushion chamber resulting from said member being out of blow-receiving relationship with said piston hammer to open to provide for conducting pressure air from said cushion chamber through said passage means.-

3. The invention set forth in claim 2 wherein:

said passage means IS in communication with said chamber for conducting pressure air directly from said cushion chamber to said chamber to act on said pressure surface in response to the opening of said check valve. 

1. In a percussion tool: a pressure fluid operated percussion motor including a housing having a cylinder bore, a piston hammer having opposed piston faces disposed in said cylinder bore for reciprocating movement, fluid distributing means for alternately valving pressure fluid to said opposed piston faces, cushioning means including a cushion chamber formed by an end portion of said cylinder bore, said piston hammer and a transverse end face closing said cylinder bore; pressure fluid supply means; a pressure fluid actuated control valve interposed between said pressure fluid supply means and said percussion motor, said control valve including a chamber and a closure member having a pressure surface located in said chamber and responsive to the admission of pressure fluid to said chamber to actuate said closure member to reduce the flow of pressure fluid to said percussion motor; passage means operable to be in communication with said cushion chamber for conducting pressure fluid from said cushion chamber to affect the admission of pressure fluid to said chamber; and, a check valve interposed in said passage means and including biasing means operable to bias said check valve in a closed position, said check valve being responsive to a predetermined pressure in said cushion chamber to open to provide for conducting pressure fluid from said cushion chamber through said passage means to cause said control valve to operate to reduce the flow oF pressure fluid to said percussion motor.
 2. In a percussion tool: a pneumatic percussion motor including a housing having a cylinder bore, a piston hammer having opposed piston faces disposed in said cylinder bore for reciprocating movement, fluid distributing means for alternately valving pressure air to said opposed piston faces, cushioning means including a pneumatic cushion chamber formed by an end portion of said cylinder bore, said piston hammer and a transverse end face closing said cylinder bore; a working member disposed to be in blow-receiving relationship with said piston hammer and axially shiftable to be out of blow-receiving relationship with said piston hammer; pressure air supply means; a fluid actuated control valve interposed between said pressure air supply means and said percussion motor, said control valve including a chamber and a closure member having a pressure surface located in said chamber and responsive to the admission of pressure fluid to said chamber to actuate said closure member to reduce the flow of pressure air to said percussion motor; passage means operable to be in communication with said cushion chamber for conducting pressure air from said cushion chamber to affect the admission of pressure fluid to said chamber; and, a check valve interposed in said passage means responsive to a predetermined air pressure in said cushion chamber resulting from said member being out of blow-receiving relationship with said piston hammer to open to provide for conducting pressure air from said cushion chamber through said passage means.
 3. The invention set forth in claim 2 wherein: said passage means is in communication with said chamber for conducting pressure air directly from said cushion chamber to said chamber to act on said pressure surface in response to the opening of said check valve. 